The present invention relates, in general, to resistance spot welding equipment and, more specifically, to spot welding electrodes containing fluid cooled welding caps or tips.
Resistance spot welding is a process commonly used to join two thin metal sheets together. A spot weld is produced by clamping two thin sheets of metal together under high pressure between two axially aligned electrodes and passing a high electrical current between the electrodes through the metal sheets. The high resistance at the interface of the two metal sheets causes heating of the sheets in an area between the contact surfaces of the electrodes. This rapid heating creates a molten zone of metal which, when cooled, forms a solid weld spot or nugget fusing the two metal sheets together.
The electrodes used to form a spot weld are typically constructed of a high electrically conductive material, such as copper. The electrodes may have an integral single piece form or may be constructed of a holder or shank portion which receives a replaceable cap or tip at one end. The caps or tips are usually of female or male configuration. The female electrode has an open mounting end whereas the male electrode contains a tapered mounting nipple. The interior of the electrode caps or tips is provided with coolant fluid flow paths for the purpose of removing heat generated during the welding operations. The holder or shank portion contains conduits for coolant fluid which flow is controlled by one hand operated main valve on single as well as multi-electrode welding machines.
During repeated spot welding operations, the elctrode caps or tips experience considerable deformation or wear at their contact surface due to the high clamping pressures required and heat generated by the current passing through the weld zone. Thus frequent reshaping or replacement of the electrode caps or tips is required in order to maintain the desired weld quality. When replacing one cap or tip, the main fluid valve needs to be shut off in order to prevent coolant fluid to flow out of the open mounting end when the cap or tip is removed. However, closing the main coolant fluid valve, particularly on multi-electrode welding machines, has the effect of shutting off coolant fluid to all the electrodes when only one or a pair of caps or tips need to be replaced. The alternative is to let the coolant fluid spill out of the open mounting end when replacing one welding cap or tip which action is both hazardous and wasteful. It would therefore be desireable to provide a spot welding electrode valve for each welding cap or tip and which would automatically regulate the coolant fluid flow during individual cap or tip replacements without affecting the cooling capacity of the other electrodes of the welding machine.